Ground operations at night, in low-visibility conditions, or at uncontrolled airports (i.e., those without an active traffic control facility) are particularly risky. Unlike during airborne operations, or during take-off and landing operations on a runway, aircraft normally taxi in close proximity to other aircraft and surface vehicles, so that the type of collision avoidance algorithms that are used for Traffic Collision Avoidance System (TCAS) or for runway collision alerting are not suited to surface operations because they would result in a high rate of unwanted alerts.
The advent of Autonomous Dependent Surveillance-Broadcast (ADS-B) systems, by which aircraft and surface vehicles transmit their own state data (identity, classification, position, velocity, track angle, etc.), and by which an aircraft may receive the state data from other aircraft and vehicles, enables the possibility of designing a system that can provide useful alerts against potential collisions. In particular, the availability of position data (latitude, longitude) derived from satellite-based Global Navigation Satellite Systems (GNSS) over the ADS-B data link allows for the prediction of the future position of an aircraft or vehicle to an accuracy which is significantly better than that available with standard TCAS systems.